Yes - the lower the power, the longer this process takes. Larger oil pumps don't seem to make any difference because it's not a lack of oil in the bearings, it's the design of the crank and the forces being applied to it due to cylinder pressure. The crankshaft has some amount of deflection - even being forged there are too many journals in too tight of a space. This has several effects - for one the journal width and therefore the ability of the journal to spread the load over a large surface area is compromised, also the lack of material between the journals and the counter-weights makes the crank really.... "floppy" - like a wet napkin. So that over time the natural deflection in the crankshaft deforms the aluminium of the case through repeated hydraulic loading of the main journal webbing.
I have had occasion to tear down a few low mileage '09-'14 WRX short blocks. The one's that are now part of the class-action suit due to premature rod bearing failure. One in particular came from a 2014 WRX with 24,000 miles on the clock. The car was essentially stock. It had intake, exhaust, and an Access Port running a stage 2 off the shelf map from COBB. Was not driven particularly hard. I tore down the short block and measured the journals with a mic and a bore gauge. Now mind you - the specs are 0.0004" to 0.0012". All three of the center journals were over 0.002" which is WAY out of spec.
Keep in mind while considering these specs that this is COLD assembly clearance. Which will effectively double at operation temp because the aluminium block expands at twice the rate of the steel crank.
The really insidious part of this is that if you go by Subaru's factory service manual, this is NOT REPAIRABLE. If it measures out of spec the whole engine block goes in the dumpster. Now - in my world we can "fix" it with a line hone. But it will happen again and you can only line hone the case ONE time - after that you have problems with oil pump fitment. The service life is directly proportional to the specific power output and how often full power is used. Obviously if you drive like grandma all the time this will never occur. But most of us don't buy/build 300 AWHP cars to not use it. We generally give people a rough sliding scale - there is no way to know what the service life will be because it depends on usage and mileage is a very poor indicator of WOT full power usage. So if I build you an STI with say... ~500 AWHP I will make it clear that you can expect 30-40k miles from such an engine. Or two to three race seasons if you are lucky.
It is also interesting to note that Subaru offers Reman engines - but ONLY for the NA models that make about 165 crank HP. This is because the turbo engine blocks aren't rebuildable without a line hone, which is not a procedure that Subaru recognizes is possible. They KNOW this. Why else would they not offer reman blocks for these cars (there is clearly an enormous demand - in fact they are offering re-manufactured turbochargers now), and why else would the diesel boxer have the main bearing webs replaced with steel inserts?
These engines were designed in the mid-80's. They were designed with a maximum displacement of 2.2 liters, and a maximum HP of 275 on the EJ20 turbo. Everything that has come after that has been pushing the envelope of the engineering to it's max.
The fix is simple - but I doubt we will ever see it. Cast the block from iron. Problem solved.
*edit* - I re-read your post and yes a larger oil pump can help offset the larger clearances. Also thicker oil. On loose engines (and by that I mean we build them with close to the max factory main journal clearance - I usually aim for *exactly* 0.001" when cold) we run 15w50 race oil and 11mm STi oil pumps. On some clapped-out 250-300k EJ25 I would probably run SAE 50 or 60 in it and put on a 12mm pump. Honestly I would. The clearances are usually ENORMOUS on the mains. I've measured high mileage 25D blocks and seen over 0.003" on the center mains.
GD